The first dose of AstraZeneca’s COVID-19 vaccine was associated with a “very small” increased risk of bleeding and other rare blood diseases, researchers say.
Results published in Nature Medicine on Wednesday stemmed from a study in Scotland involving 2.53 million people who received the first doses of COVID-19 vaccines between December 8 and April 14 and included 57.5% of the country’s adult population . Of the total, about 1.7 million people received the AstraZeneca vaccine, and about 820,000 received the Pfizer vaccine.
While the AstraZeneca COVID-19 vaccine has not yet been approved for use in the United States, an independent committee advising vaccinations in the UK has previously recommended people aged 1
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Researchers reported an increased risk of abnormally low platelet counts within six days of vaccination with AstraZeneca’s product. There were 1.33 more events with thrombocytopenia per 100,000 than expected. Researchers also found an incidence of 1.13 cases per 100,000 of so-called idiopathic thrombocytopenic purpura (ITP) or a blood disease that involved an abnormal decrease in the number of platelets per Hopkins Medicine. ITP was “most pronounced” about 21 to 27 days after vaccination, but was seen seven days after vaccination.
“This very small risk is important, but should be seen in the context of the very clear benefits of the ChAdOx1 vaccine,” the authors wrote.
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The problem was more commonly found among older adults; researchers noted ITP during the AstraZeneca period after vaccination for 40-49-year-olds 0.62 more events than expected per. 100,000 doses, and in the adults studied, there were 0.46 more events than expected per 100,000 doses.
Study authors reported 22 patients with the abnormal drop in platelet count, although nearly half had previous prescriptions that could cause the problem. The study suggests that very few ITP patients were prescribed ITP therapies after receiving the AstraZeneca vaccine.
Researchers noted three deaths after ITP, but not due to ITP, and the deaths occurred in both vaccinated and non-vaccinated people over the age of 70.
“The first dose of ChAdOx1 was found to be associated with small increased risks of ITP with indicative evidence of an increased risk of arterial thromboembolic and haemorrhagic events. Given these small increased risks of ChAdOx1, alternative vaccines for individuals with low COVID-19 risk may be justified when the supply allows, “the authors of the study wrote.
The increased risk of so-called arterial thromboembolic events occurred within 27 days of receiving the AstraZeneca vaccine, although fewer cases appeared than expected (3,288 versus 3,328), and haemorrhagic or bleeding events occurred within 27 days of vaccination, although fewer cases was observed than expected (301 vs. 349).
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No such problems were found with Pfizer’s vaccine.
Researchers could not draw firm conclusions about an association with coagulation problems, including the rare but deadly cerebral venous sinus thrombosis, CVST. Six cases of CVST have occurred in vaccinated individuals with AstraZeneca’s product, and researchers suspected that the result is likely to be “extremely rare.”
Research authors suggested public health officials inform people about the “relatively small increased risks associated with” AstraZeneca’s vaccine.